When it comes to matters of law, are arguments for deterrence distinct from arguments about morality? Are practical concerns separate from moral judgment?
It seems one thing to say "we should outlaw murder so as to prevent murder" and another to say "we should outlaw murder because it is wrong".
-ace

The two statements in quotes are surely different. But the first can also express a moral standpoint: that it is morally important to achieve a low murder rate. This moral standpoint is reflected in various more specific claims.

1. We should not inflict punishment or pain on anyone unless doing so produces some good for others (e.g., by preventing the person from offending again or by deterring others).

2. We should inflict pain whenever doing so produces some greater good for others.

This second claim is highly problematic insofar as it may justify "punishing" the innocent when doing so helps deter real criminals. For this reason, those who hold deterrence to be morally important often claim instead:

3. In deciding how severely to punish specific types of crime, we should take into account how much of an impact greater severity would have on the frequency of this crime.

This third claim is consistent with the idea that people may be punished only for having done something wrong. But it allows two kinds of conduct that are equally wrong to be punished differently. One crime is punished lightly, yet some equally bad crime is punished more severely because here such punishment is more effective in getting the crime rate down. Moral arguments are made both for and against this claim.